Among the various desired performance objectives for personal care absorbent products is low leakage from the product after insult and a dry feel to the wearer or user. Absorbent articles commonly fail before the total absorbent capacity of the product has been utilized. Absorbent garments, such as incontinence garments and disposable diapers, often leak at the legs and the waist. The leakage can be the result of a variety of shortcomings in the product; one particular one being insufficient fluid uptake by the absorbent system, particularly during high liquid volume insults or on the third liquid insult.
It has been found that urination can occur at rates as high as 15 to 20 milliliters per second and velocities as high as 280 centimeters per second. Conventional absorbent articles may initially uptake fluid at a rate of only 8 milliliters per second or less. In addition, the initial uptake rates for conventional absorbent structures can deteriorate after receiving prior liquid surges into their structures. The disparity between liquid delivery and uptake rates can result in excessive pooling on the surface of the absorbent fabric before the liquid is taken-up by the absorbent core. During this time, pooled liquid can leak from the leg openings of the diaper and soil the outer clothing and/or the bedding of the wearer. Attempts to alleviate this leakage have included providing physical barriers with such design features as elastic leg gathers, as well as changing the amount and/or configuration of the absorbent material in the zone of the structure into which the liquid surges typically occur. Absorbent gelling particles such as superabsorbent polymers have also been included to increase the liquid holding capacity in various regions of the absorbent structure; such absorbent gelling particles, however, may not have the rapid uptake rates of conventional materials such as wood pulp and fluff which are also commonly used in absorbent cores. As a result, as the amount of absorbent gelling particles in the absorbent core structures are increased in modern day diapers, oftentimes the initial uptake rate will tend to decrease.
One important component of many personal care products is the fluid surge management layer, which is typically placed under the liner and above a superabsorbent layer. The surge management layer (also referred to as the surge layer, surge material, intake layer, transfer layer, transport layer, and the like) manages the flow of fluids to the superabsorbent layer. Fluid management is generally measured by the properties of void volume and permeability. If the surge material permeability is too high, the fluid will permeate the superabsorbent material too quickly, causing it to be overwhelmed. If permeability is too low, the fluid will not progress to the superabsorbent material and can “back-up” and pool into and on the liner. The surge management layer should also have a sufficient void volume to provide temporary storage for incoming liquid.
Conventional surge materials include biodegradable and non-biodegradable fibers to achieve the desired processability and physical properties, such as void volume, compressability, resiliency, and permeability. Conventional methods of producing such surge materials have included bonded carded web processes, which produce a nonwoven web.
The bonded carded web process generally requires the use of staple cut fibers, typically in a length of approximately 1 to 3 inches. In order to give the nonwoven web integrity after processing, at least one of the fiber components includes a thermoplastic material that is at least partially melted or softened to bind the web together to make a cohesive layer. Such a component is commonly referred to as a binder fiber.
One shortcoming of the bonded carded web process involves the collapse of the web during or after bonding at elevated temperatures, resulting in a nonwoven web having inferior intake properties. Web collapse can occur during bonding due to the relatively high temperatures used to soften and partially melt at least one of the fiber components. Web collapse can also occur due to the mechanical force required to either pass hot air through the web structure or compress the web structure against one or more rolls or conveyors. Additionally, web collapse can occur when the web is wound into a roll after bonding. The hot fibers may still be soft and pliable (e.g., above the glass transition temperature for the particular fibers), and the internal pressures of the roll can cause the web to collapse. As the web cools inside the roll, the fibers will slowly conform to their existing spatial alignment until the temperature reaches or falls below the glass transition temperature.
As such, a need in the industry exists for a nonwoven web for use in a surge management layer in an absorbent article, the nonwoven web having a bulky, resilient structure and possessing the various desired properties described above.